Commit f6883df6 authored Mar 20, 2024 by Pawan Gupta Committed by Ma Wupeng Mar 20, 2024

x86/mmio: Disable KVM mitigation when X86_FEATURE_CLEAR_CPU_BUF is set

stable inclusion
from stable-v6.6.22
commit c35ca0968de41952af2ad7d22881e4a7c6e1b145
bugzilla: https://gitee.com/openeuler/kernel/issues/I99TJK

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c35ca0968de41952af2ad7d22881e4a7c6e1b145



--------------------------------

commit e95df4ec0c0c9791941f112db699fae794b9862a upstream.

Currently MMIO Stale Data mitigation for CPUs not affected by MDS/TAA is
to only deploy VERW at VMentry by enabling mmio_stale_data_clear static
branch. No mitigation is needed for kernel->user transitions. If such
CPUs are also affected by RFDS, its mitigation may set
X86_FEATURE_CLEAR_CPU_BUF to deploy VERW at kernel->user and VMentry.
This could result in duplicate VERW at VMentry.

Fix this by disabling mmio_stale_data_clear static branch when
X86_FEATURE_CLEAR_CPU_BUF is enabled.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>

parent 315203a2

arch/x86/kernel/cpu/bugs.c

+12 −2

Original line number	Diff line number	Diff line
		@@ -422,6 +422,13 @@ static void __init mmio_select_mitigation(void)
		if (boot_cpu_has_bug(X86_BUG_MDS) \|\| (boot_cpu_has_bug(X86_BUG_TAA) &&
		boot_cpu_has(X86_FEATURE_RTM)))
		setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);

		/*
		* X86_FEATURE_CLEAR_CPU_BUF could be enabled by other VERW based
		* mitigations, disable KVM-only mitigation in that case.
		*/
		if (boot_cpu_has(X86_FEATURE_CLEAR_CPU_BUF))
		static_branch_disable(&mmio_stale_data_clear);
		else
		static_branch_enable(&mmio_stale_data_clear);

		@@ -498,8 +505,11 @@ static void __init md_clear_update_mitigation(void)
		taa_mitigation = TAA_MITIGATION_VERW;
		taa_select_mitigation();
		}
		if (mmio_mitigation == MMIO_MITIGATION_OFF &&
		boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA)) {
		/*
		* MMIO_MITIGATION_OFF is not checked here so that mmio_stale_data_clear
		* gets updated correctly as per X86_FEATURE_CLEAR_CPU_BUF state.
		*/
		if (boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA)) {
		mmio_mitigation = MMIO_MITIGATION_VERW;
		mmio_select_mitigation();
		}